[unreadable] Artificial valves have been used to replace diseased human heart valves for more than four decades. Thrombus deposition and ensuing complications remain significant with implanted mechanical valves and the patients require long-term anti-coagulant therapy. In tissue valves, the leaflets exhibit structural alterations and tear due to fatigue failure requiring replacement surgery in about 10-12 years. Large flexure stresses during the opening and closing have been implicated in structural alterations and leaflet tear. In vitro experiments have yielded limited, but valuable information on the stresses on the leaflets during the valve function. With the advent of high-speed computing capabilities, computational fluid dynamic (CFD) analysis has been used to study the valve flow dynamics in detail. Finite element (FE) structural analysis has also been employed to analyze for the stress distribution on the leaflets with static and dynamic pressure loads and the results have been correlated with zones of structural failure and leaflet tear. Development of a rigorous fluid-structure interaction (FSI) analysis coupling the fluid flow with the corresponding leaflet motion is very important in the accurate simulation of valve function during a cardiac cycle. The goal of this project is to develop a three-dimensional (3D) simulation of unsteady flow through bioprosthetic valves incorporating a rigorous fluid-structure interaction algorithm. The CFD analysis will employ the state-of-the-art arbitrary Lagrangian-Eulerian (ALE) technique employing arbitrarily shaped elements. Experimentally derived non-linear constitutive model for the aortic valve cusps will be incorporated in the FE analysis. FSI algorithm will be developed to couple the interaction between the fluid and the valve leaflet and the simulation results will be validated with data on the leaflet deformation and fluid velocity measured from in vitro experiments on bioprosthetic valves. The FSI simulation, once validated, can be used to compute the stresses developed during the opening and closing phases on the tissue valves. It will be further employed to assess the effect of geometric changes and tissue preservation towards minimizing the flexure stresses during the valve function in order to improve the durability of the bioprostheses. The deliverable end product of this project will be a physiologically realistic, tissue valve simulation incorporating a validated FSI algorithm. The simulation will have the potential for significant improvement in the prosthetic valve designs towards improved functionality. [unreadable] [unreadable]